Shadow mask perforated along intersection of side wall and reinforcing flange

ABSTRACT

In a shadow mask comprising a rectangular mask plate and a rectangular frame member including a rectangular side wall for supporting the mask plate and a reinforcing flange bent inwardly at right angles with respect to the side wall, there are provided a plurality of perforations along a border line between the side wall and the reinforcing flange.

United States Patent 91 Tsuneta et al.

[ 51 Jan. 9, 1973 [54] SHADOW MASK PERFORATED ALONG INTERSECTION OF SIDE WALL AND REINFORCING FLANGE [75] Inventors: Asahide Tsuneta, Kawasaki; Shinichi Sawagata, Tokyo, both of Japan [73] Assignee: Tokyo Skibaura Electric Co.,

Kawasaki-shi, Japan [22] Filed: July 26, 1971 21 App]. No.: 164,801

[30] Foreign Application Priority Data July 3, 1970 Japan ..45/7534l [52] US. Cl. ..3l3/85 S, 29/25.l8, 313/348 [51] Int. Cl. ..H0lj 29/06, l-lOlj 29/02, l-lOlj 29/08 [58] Field of Search ..3l3/85 S, 92 B, 92 PD [56] References Cited UNITED STATES PATENTS 2,795,718 6/1957 Van l-lekken et al ..3l3/85 S 3,387,159 6/1968 Schwartz et al. ..313/85 S Primary Examiner-Robert Segal Attorney-R. D. Flynn et al.

[57] ABSTRACT In a shadow mask comprising a rectangular mask plate and a rectangular frame member including a rectangular side wall for supporting the 'mask plate and a reinforcing flange bent inwardly at right angles with respect to the side wall, there are provided a plurality of perforations along a border line between the side wall and the reinforcing flange.

6 Claims, 5 Drawing Figures SHADOW MASK PERFORATED ALONG INTERSECTION OF SIDE WALL AND REINFORCING FLANGE This invention relates to a shadow mask for use in color television receiving tubes, and more particularly to an improved construction of a frame member for fixing a mask plate in place.

A color television receiving tube generally comprises an envelope having a funnel including a neck, and a face plate joined to the opening of the funnel. On the inside of the face plate is provided a mask plate having a plurality of perforations that control passage of electron beams from electron guns which are contained in the neck. Generally, the mask plate is in the form of a rectangular curved surface having at least one center of curvature on the side of the electron guns. The curvature coincides with that of the curved inner surface of the face plate coated with phosphors and it is desired that the spacing between the inner surface of the face plate and the surface of the mask plate should be equal at all points. Furthermore, since it is necessary to make extremely thin the metal plate that comprises the face plate, the mask plate is secured to a rectangular frame member having sufficiently high mechanical strength to resist deformation and the frame member is removably fixed to a mounting member secured to projections extending from the periphery of the face plate so as to prevent deformation of the mask plate.

One method of fabricating the rectangular frame member is as follows. A metal strip having a suitable thickness, for example 2.6 mm, is prepared and the metal strip is bent 90 along its longitudinal axis to have a generally L-shaped cross-section. The L shaped metal strip is then bent transversely at four spaced apart points and the opposite ends of the strip are then joined together, such as by welding, thus forming a flat and rectangular frame member. To securely fix the mask plate in place, the rectangular frame member is then deformed by means of a press or the like into a curved configuration of the same curvature as that of the periphery of the mask plate. The frame member is then subjected to a suitable heat treatment in order to remove the strain caused by the working operations described above. However, some strain still remains unremoved. During the evacuation step of the envelope following the incorporation of the shadow mask assembly comprising the mask plate secured to the frame member into the envelope of the receiving tube, the shadow mask is heated to a temperature of about 450C. Due to the residual strain not removed even by this heat treatment the frame member has a tendency to twist about its normal axis. Such twisting causes the mask plate to deform after completion of the receiving tube, increasing the chance of creating the so-called misslanding, whereby the electron beams fail to correctly irradiate the phosphor dots of red, blue and green, for example, applied on the inner surface of the face plate, thus causing color break-up of the picture image. For this reason, it is highly desirable to provide an improved rectangular frame member capable of decreasing the strain caused by the working operations.

in the color television receiving tube including a plurality of phosphor dots formed on the inner surface of the face plate the so-called black matrix type tube has been developed in which the diameter of the perforations of the mask plate for controlling the passage of the electron beams is made larger than that of the dots. For this purpose, after forming the phosphor dots, the shadow mask is removed from the face plate and is then dipped in an etching solution to enlarge the diameter of the perforations to be greater than that of the phosphor dots. The etching solution remaining at the bent portions of the rectangular frame member after the etching treatment tends to corrode, oxidize and rust the frame member and fine particles formed by such chemical reactions tend to close the perforations.

Therefore, it is desirable to obtain an improved rectangular frame member capable of preventing the retention of the residual etching solution.

Accordingly, it is an object of the invention to provide an improved shadow mask for a color television receiving tube having a rectangular frame member of a configuration which has a lesser tendency of preserving the strain created by mechanical working operations and which prevents the etching solution from remaining.

Another object of this invention is to provide an improved shadow mask having means to effectively absorb internal strain of the rectangular frame member, thus eliminating the necessity of carrying out the strain removing heat treatment.

SUMMARY OF THE INVENTION According to this invention, there is provided a shadow mask for use in a color television receiving tube comprising a rectangular mask plate including a curved face having at least one center of curvature on the side of a source of electron beams contained in the envelope of the receiving tube and provided with a plurality of fine perforations for controlling the passage of the electron beams, and a peripheral flange surrounding the curved face and bent toward the source of electron beams; and a rectangular frame member for supporting the mask plate, the rectangular frame member including a rectangular side wall to receive said peripheral flange and a reinforcing flange bent inwardly at right angles with respect to the side wall, the free edge of the side wall being curved by the same radius of curvature as that of the periphery of the mask plate, characterized in that there are provided a plurality of spaced apart perforations along a border line between the reinforcing flange and the side wall and that each of the last mentioned perforations encompasses both the reinforcing flange and the rectangular side wall.

The perforations provided along the border line not only make it easy to longitudinally bend the metal strip into an L shaped cross-sectional configuration but also absorb internal strain created in the rectangular frame member at the time of its various bending operations,

thus eliminating the expensive annealing treatment for removing the residual internal strain for a frame member of small size.

Similar perforations may also be provided at the corners of the rectangular frame member to attain the same purpose. Further, these perforations along the border line and at the comers are not only effective to drain the etching solution used for etching the shadow mask but also are used to hold in position a metal foil used to prevent passage of undesirable electron beams.

The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 shows a side view, partly broken away, of a color television receiving tube employing the shadow mask embodying the invention;

FIG. 2 is a perspective view, partly broken away, of the shadow mask shown in. FIG. 1;

FIG. 3 is a bottom plan view of the shadow mask shown in FIG. 2;

FIG. 4 shows a partial perspective view of a modified shadow mask including a metal foil for preventing the passage of undesirable electron beams and mounted in the face plate of a receiving tubes; and

FIG. 5 shows an enlarged sectional view taken along a line V-V in FIG. 4.

The envelope of a color television receiving tube shown in FIG. 1 comprises a funnel 2 having a neck containing a source of electron beams l, a face plate 7 and a shadow mask 6 removably mounted in the face plate by means of pins 4 secured to the peripheral flange 3 of the face plate. The peripheral flange 3 is joined at 8 to the opening of the funnel by means of a low melting-point glass, for example. A plurality of phosphor dots (not shown) adapted to emanate red, blue and green, respectively when impinged upon by the electron beams are formed on the inner surface 9 of the face plate by coating for example. The face plate 7 is generally rectangular and its inner surface 9 is in the form of a curved surface having at least one center of curvature located on the side of the source of electron beams.

As shown in FIGS. 2 and 3, shadow mask 6 is provided with a plurality of small perforations 11 for controlling the passage of the electron beams impinging upon the phosphordots. The inner surface of the shadow mask has the same radius of curvature as the inner surface 9 of the face plate. The shadow mask comprises a rectangular mask plate 13 with a peripheral flange l2 bent in the direction toward the source of electron beams l and a rectangular frame member 14 adapted to securely support the mask plate 13.

The frame member 14 comprises a vertical side wall 15 adapted to support the mask plate and a horizontal reinforcing flange 16 bent inwardly at about 90. The upper edge (as viewed in FIG. 2) of the vertical side wall 15 is curved with the same radius of curvature as that of the periphery of mask plate 13 and the outer surface of the vertical side wall 15 is welded to the peripheral flange 12 of the mask plate 13.

A plurality of perforations 19 are formed along the border line 18 between horizonal reinforcing flange l6 and vertical side wall 15 to encompass portions of the flange 16 and side wall 15. Such perforations 19 can also be formed at four corners of the frame member to encompass portions of the larger side 20 and shorter side 21 of the vertical side wall 15. Uniform spacing between adjoining perforations 19 is advantageous for removing the stress but the spacings may not necessarily be uniform.rPerforations 19 at the corners of the rectangular frame member 14 are effective to drain remaining etching solution which is used to etch the shadow mask.

Mask plate 13 may be formed by press working a thin metal plate. One example of manufacturing rectangular frame member 14 is as follows. First, a metal strip having a predetermined length and width is prepared. A plurality of rectangular perforations 19 are punched out along a longitudinal line 18 along which the metal strip is to be bent. The configuration of the perforations 19 is not limited to rectangular but may be of any other desired shape. The strip is bent into an L shaped cross section along line 18 which passes substantially through the center of perforations 19, by means of a suitable bending machine. The metal strip is then bent at four spaced apart points into a rectangular configuration, and the opposite ends of the metal strip are butt welded. Then, the resulting frame member is bent to have the same radius of curvature as the periphery of mask plate 13. Peripheral flange 12 of mask plate 13 is fit over vertical side wall 15 and is then welded thereto. The internal stress created in the frame member due to the processsteps described above is adsorbed by perforations 19, thus providing a frame member having a very low internal strain. For this reason, it is not necessary to heat anneal the frame member if it is of comparatively small size. Further, as above described, the perforations are effective to drain the remaining etching solution. Whilerespective perforations deform slightly by the adsorption of the stress such deformation does not affect in any way the operating characteristics of the shadow mask.

FIGS. 4 and 5 show a portion of a modified shadow mask together with a portion of face plate 7 wherein a foil of metal 23 such as aluminum is provided to prevent passage of undesirable or useless electron beams. The metal foil 23 takes the form of a rectangular strip having a central opening of substantially the same area as the central opening in the horizontal flange 16 of the rectangular frame member 14. The inner portion of the metal foil overlies horizontal flange 16 and is secured thereto by means of a plurality of U shaped clamps 25 whereas the outer portion extends outwardly of horizontal flange 16. Each one of clamps 25 is provided with a projection 26 received in one of the perforations 19 so as to firmly hold the metal foil. The outer edge of metal foil 23 is in sliding engagement with the inner surface of flange 3 of the face plate to prevent electron beams from passing into the gap between the face plate and the rectangular frame member 14. Heretofore, metal foil 23 was welded to frame member 14 but the welding spark tends to close the perforations of the mask plate provided for controlling the passage of the electron beams. Accordingly, it has heretofore been necessary to provide means for preventing the adverse effects of the welding spark. According to this embodiment, the welding operation is not necessary.

What we claim is:

l. A shadow mask for use in a color television receiving tube comprising a rectangular mask plate including a curved face having at least one center of curvature on the side of a source of electron beams contained in the envelope of said receiving tube and provided with a plurality of fine perforations for controlling the passage of said electron beams, and a peripheral flange surrounding said curved face and bent toward said source of electron beams; a rectangular frame member for supporting said mask plate, said rectangular frame member including a rectangular side wall to receive said peripheral flange and a reinforcing flange bent inwardly at right angles with respect to said side wall, the free edge of said side wall being curved by the same radius of curvature as that of the periphery of said mask plate; and a plurality of spaced apart perforations provided in said rectangular frame member along a border line between said reinforcing flange and said side wall, each of said last mentioned perforations encompassing both of said reinforcing flange and said rectangular side wall.

2. A shadow mask as claimed in claim 1 wherein perforations of said rectangular frame member are also provided at the corners of said rectangular side wall.

3. A shadow mask as claimed in claim 1 which further comprises a rectangular metal foil for preventing passage of undesirable electron beams, the inner portion of said metal foil overlapping said reinforcing flange and being secured to said perforations of said rectangular frame member, and the outer portion of said metal foil extending outwardly from said reinforcing flange.

4. A shadow mask as claimed in claim 3 wherein said inner portion of said metal foil is secured to said reinforcing flange by means of U shaped clamps.

5. A shadow mask as claimed in claim 1 wherein said perforations of said rectangular frame are generally rectangular.

6. A shadow mask as claimed in claim 1 wherein said perforations of said rectangular frame are uniformly spaced from each other. 

1. A shadow mask for use in a color television receiving tube comprising a rectangular mask plate including a curved face having at least one center of curvature on the side of a source of electron beams contained in the envelope of said receiving tube and provided with a plurality of fine perforations for controlling the passage of said electron beams, and a peripheral flange surrounding said curved face and bent toward said source of electron beams; a rectangular frame member for supporting said mask plate, said rectangular frame member including a rectangular side wall to receive said peripheral flange and a reinforcing flange bent inwardly at right angles with respect to said side wall, the free edge of said side wall being curved by the same radius of curvature as that of the periphery of said mask plate; and a plurality of spaced apart perforations provided in said rectangular frame member along a border line between said reinforcing flange and said side wall, each of said last mentioned perforations encompassing both of said reinforcing flange and said rectangular side wall.
 2. A shadow mask as claimed in claim 1 wherein perforations of said rectangular frame member are also provided at the corners of said rectangular side wall.
 3. A shadow mask as claimed in claim 1 which further comprises a rectangular metal foil for preventing passage of undesirable electron beams, the inner portion of said metal foil overlapping said reinforcing flange and being secured to said perforations of said rectangular frame member, and the outer portion of said metal foil extending outwardly from said reinforcing flange.
 4. A shadow mask as claimed in claim 3 wherein said inner portion of said metal foil is secured to said reinforcing flange by means of U shaped clamps.
 5. A shadow mask as claimed in claim 1 wherein said perforations of said rectangular frame are generally rectangular.
 6. A shadow mask as claimed in claim 1 wherein said perforations of said rectangular frame are uniformly spaced from each other. 